Geographic Range

Western rock lobsters can only be found in the Indo-West Pacific Ocean region. They are restricted primarily to the west coast of Australia between the Northwest Cape and Hamelin Harbour, but they can also be found at some of the offshore islands. (Holthius, 1991)

Habitat

Panulirus cygnus live as free-swimming larvae in the ocean for the first year of their life. Newly hatched, they can live up to 1,500 kilometers from the coastline. As they grow, they return to the coast to live for approximately five years on the reefs in water 40 meters deep, or less. After this period, they migrate to reefs that are deeper and further away from the shore. During this new stage of their life, the Western rock lobster is found in depths between 0-90 meters, and rarely as deep as 120 meters. As adults, they are nocturnal, so during the day they use coral and rock crevices for shelter. (Holthius, 1991; Phillips, 2002)

Physical Description

The basic physical features of the Western rock lobster are: compound eyes on mobile stalks, antennae, six pairs of small limbs around the mouth, and five pairs of walking legs. (Taylor, 2002)

Panulirus cygnus also have a strong and muscular abdomen with an exoskeleton that is segmented on their backs. They have swimmerets underneath the tail which ends in a tail fan. Their body color is pale to dark purple-brown with pale spots on the abdomen. The antennulae and legs are uniform in color with pale streaks. (Holthius, 1991; Taylor, 2002)

Western rock lobsters have a maximum mass of 5 kilograms, and the largest ever reported was 5.5 kilograms, or about 12 pounds. The average length of their carapace is 8-10 centimeters, but their body is 9-11 centimeters long in ovigerous females and lobsters with spermatophores. The main distinction between different species of lobster can be made from their abdominal somites. In Panulirus cygnus there are pubescent grooves on the dorsal surface of the somites and there is a pubescent area along the posterior region. (Holthius, 1991; Phillips, 2002)

As for sexual dimorphism, there are three main distinguishing characters between males and females. The first is the fifth pair of walking legs. In females the pair ends in a small claw, and in males, the pair ends in a point without a claw. The second difference is the location of the genital pore. At the base of the third pair of legs is the genital pore for the females, whereas in males, the genital pore is at the base of the fifth pair of legs. The third difference is between the pleopods/swimmers on the Rock lobsters' tails. In a female there are inner and outer pleopods used to carry her eggs; a male simply has four pairs of single pleopods.

Another related issue to sexual dimorphism in Panulirus cygnus is the hormones that are secreted by androgenic glands to induce the development of male sex characters. Also called the glands that make the male, the androgenic glands not only have an effect on males, they also have an effect on females. If they are artificially implanted into a female Western rock lobster, her ovaries will begin to turn into testes. As a result, not only will she start to produce sperm, but during the next molt her appendages will be reformed with male characteristics (such as are mentioned above). (Bliss, 1982; Hickman, et al., 2003; PIRSA, 1999)

Also, lobsters lower their metabolic rate when they are cooled, and as a result, their responses are altered. (Paterson, 1996)

Development

It takes about 1 year for Panulirus cygnus to complete its entire larval cycle. During the larval cycle there are about 11 complex stages. At the end of a year, the juvenile rock lobsters are considered puerulus. In this puerulus stage, they are normally 25 millimeters long, and look like minature adult lobsters. In this stage they have an unusually low sensitivity to temperature changes, which works as an energy saving adaptation. In the puerulus stage they drift back to the coast and sink to the bottom where they stay for 2 or 3 years while they slowly mature. In this stage, the rock lobster could possibly grow 4 centimeters per year, which is very rapid. This rapid growth slows down as the lobster ages. The rock lobsters reach their full size at around 10 years of age. (Phillips, 2002; Imgrund, 1999/2000; Anger and Vonk, 2001)

Western rock lobsters must, like many crustaceans, shed their exoskeleton in order to grow. Molting occurs frequently in the younger ages, and approximately one or two times a year in maturing lobsters. The lobsters will hide for a few days after they molt because they have a new soft shell and are defenseless against predators. It is also a possibility that the lobsters may eat what they molt so they can retain the calcium in it to aid in forming their new shell. (Imgrund, 1999/2000)

Reproduction

It is a very difficult task to see lobsters mating in the wild because they have very private habits and remain hidden under rocks. When they do come out it is at night, because they are nocturnal, so it is difficult to watch their behavior in their natural environment without affecting their actions in any way. Despite the setbacks, scientists do know a few things about the mating systems of lobsters in general. The knowledge that they have was acquired from laboratory observations in artificial habitats. (The Lobster Conservancy, 1998)

When the time is approaching for the females to shed their shells, they initiate this pairing by repeatedly going to where the male lobster lives. The pair lives together for a couple days and when the females are about to molt they jab the male they are living with. The male Panulirus cygnus approach the soft females, and turn them over onto their backs. The males proceed to put their ventral surface to the females in a head-to-head fashion. Spermatophores emerge from the male's genital opening and the male rock lobsters transfer a packet of sperm to the females, and stick this jelly-like fluid matrix of sperm between her last pair of legs. It appears as a tar spot. The freshly placed sperm go into the oviduct of the females, and as the fluid matrix disappears, the sperm are released to fertilize the female's eggs. This whole mating process takes about 30-60 seconds. (Bliss, 1982; Taylor, 2002)

In a day or two the female lobsters move to a different shelter to finish hardening their shells. No sooner do the females leave the males' shelter, does another female move in to go through the same process she just completed. This goes on until all the females in that male's area have their eggs fertilized. For females, mating is serial monogamy because only one exclusive pair is formed during each breeding season. However, for males, mating is serial polygyny because they form exclusive bonds with a series of females during each breeding season. (The Lobster Conservancy, 1998)

The breeding season for adults is during the late winter. They generally spawn for the first time between the ages of 6 and 7. The females have a final pre-spawning molt and then wait for optimum weather and food conditions. It is possible that the lunar cycle or rising water temperature produce the biological urge for courtship. (Phillips, 2002; Imgrund, 1999/2000; Monchaux, n/a)

The eggs are laid between September and January and depending on the size of the female, 300,000-700,000 eggs are produced. Over a number of weeks the eggs develop inside the mother until the cephalothorax is filled with a bright orange, caviar mass. (Imgrund, 1999/2000)

Once hatched, the rock lobster larvae, phyllosoma, go to the surface with the other planktonic animals. They move by the current of the ocean, or by attaching to a jellyfish. Understandably, morality rates are very high during this 9-11 month time period. (Phillips, 2002; Griffin, 2001; Imgrund, 1999/2000)

The eggs are eventually laid, after 3-4 hours of work, through holes at the base of the third pairs of legs. When the eggs are laid, they are attached to the setae (fine hairs) on the abdominal swimmerets of the females. The females carry the eggs while they develop for a maximum of 95 days, and then they hatch. Females carrying eggs are called, berried, because the appearance of the developing eggs is similar to that of berries. Once the eggs are hatched, the mothers leave the babies to fend for themselves. (Imgrund, 1999/2000)

Lifespan/Longevity

Scientists have yet to find a reliable way to determine the age of lobsters. Nonetheless, they can make guesses based on geographical location, and the temperature of the water, among other things. It is thought that lobsters can live in the wild for 100 years or more. But, it is expected that average lobsters only live to be 30 years old in the wild. However, in a marine research laboratory aquarium, the oldest rock lobster to survive was 28 years old, had a 165mm carapace, and weighed 7 pounds. (Phillips, 2002; Cornish, 2000)

Although, the number for the average age of lobsters is skewed - lobsters that reach that age are very lucky. Of all the eggs that the females release, only 1/10 of 1% survives for more than a few weeks. For example, if a female laid 10,000 eggs, 10 would survive. (Gulf of Maine Aquarium, 1998)

Range lifespanStatus: wild

100 (high) years

Range lifespanStatus: captivity

28 (high) years

Average lifespanStatus: wild

30 years

Behavior

In the Western Australian species of rock lobster, the phyllosoma are transported into the Indian Ocean by currents before molting into a stage looking very similar to a translucent mini-adult. In this stage the lobsters swim across the continental shelf to settle in shallow inshore reefs. But, soon the Panulirus cygnus migrates from the inshore reefs to deeper waters so they can spawn. This is called the whites run because the lobsters are still white from their most recent molt. When migrating, they can travel great distances. 60-100 fathoms is possible, or maybe 4 kilometers a day. (Taylor, 2002)

Communication and Perception

There have been many studies done about the visual senses of Panulirus cygnus. These lobsters have eyes on eyestalks on their heads. They use them to see, but tests have been done that prove that they do not necessarily need their eyes to know where to go. Scientists believe that, like birds, lobsters may be using the Earth's magnetic field to find their way around. (Popper, et al., March 2001; )

It is also known that Western rock lobsters have special sound producing structures to produce acoustic signals. Panulirus cygnus produce a very unpleasant noise in a fascinatingly individual way. Similar to a violinist, they slide a bow across a vibrating surface. The bow is called the plectrum which is at the base of each antenna, and the vibrating surface is the file, a lump on both sides of a lobster's head. The lobsters simply wave their antennae and the sound produced is a loud, scratchy buzz. The technique is known as the stick-and-slip motion and the key to sound production is friction. The friction comes from microscopic shingles on the files of the lobsters. Hence, the longer the file, the longer time the lobsters can produce their sound. (Popper, et al., March 2001; Summers, 2001)

Scientists believe that lobsters make these noises to startle predators enough to scare them away. This tactic is especially useful during the time right after molting. It appears that this feature of being able to produce the sound even when soft-bodied is an evolutionary response to predation. Protecting themselves in their most vulnerable time is very important. (Summers, 2001; Meredith, 2001)

However, not much is known about their sensitivity to vibration. It is hypothesized that the way lobsters interpret the acoustic signals they receive is by tiny structures in their inner ear called stereocilia. When the sound reaches the ears of the lobsters it shakes the eardrum which displaces the endolymphatic fluid in the inner, and deflects the stereocilia. The stereocilia then convert the sound into nerve impulses. However, scientists believe that lobsters cannot hear unless at very close range, so they have come to the conclusion that their sound production is not intended to help them communicate with their own species, but instead to talk to other species. As a matter of fact, it is believed that the lobsters can't even hear the sounds they produce. (Popper, et al., March 2001; Noca, et al., 2000; Summers, 2001; Meredith, 2001)

Additionally, Panulirus cygnus also communicate by the use of chemical signals or pheromones. They release these in their urine through little holes found at the base of their antennae. These pheromones are carried by currents to nearby lobsters who use their chemoreceptors (on their antennules) to detect the signals. Scientists suppose that males and females have different pheromones in their urine, which allow rock lobsters to distinguish between male and female in other rock lobsters. Other uses for the chemical signals are not yet known. (Raethke, 2001)

Food Habits

As the lobsters get older and move to the reefs, they also change their feeding habits. They begin to go out at night and search for food. In one night, a lobster is said to cover a mile or more a night looking for food. Panulirus cygnus are considered to be omnivorous, eating both animal and plant materials. They eat mollusks, worms, crabs, clams, sea urchins, slow flounder, seaweed, and seagrasses. A lobster will even eat another lobster if they have the chance. In cages lobsters can be cannibalistic, but this has never been seen in the wild. (Holthius, 1991; Imgrund, 1999/2000; Gulf of Maine Aquarium, 1998)

Predation

Humans are the biggest predators of the Western rock lobsters. Octopus, snapper, jewfish, and sharks are also their predators. But, to help minimize the number of potentially fatal attacks they are cryptic and they hide in rock crevices during the day. Panulirus cygnus can also avoid capture by their aquatic predators by producing a startling buzzing noise or self-amputating a limb. The limb occupies the predator and the lobsters are able to make their escape. However, problems arise with this approach because the ability to find food is reduced as limbs are lost. Luckily, the sacrificed limb is replaced during the next molt. (Imgrund, 1999/2000; Monchaux, n/a; Taylor, 2002; Meredith, 2001)

Ecosystem Roles

While the lobsters are settled on the ocean floor they co-exist with the other bottom-dwellers. The other species that they live with are things such as: sea urchins, crabs, mussels, and algae. But, lobsters are considered to be bad neighbors because they will not hesitate to eat anything that lives around them, if they have the opportunity. (Gulf of Maine Aquarium, 1998)

A while ago, sea urchins flourished and consumed large areas of kelp on the ocean floor, making it a very open area. But, as a result of a demand for sea urchins, their population has been reduced and the kelp is beginning to grow back. Scientists think that the growth of this new kelp provides places for young lobsters to hide and as a result is helping the population to grow. (Gulf of Maine Aquarium, 1998)

Economic Importance for Humans: Positive

Panulirus cygnus are seen as one of the best and most desired seafoods in the world and in Australia, Western rock lobsters are the richest commercial fishing industry. Each year, 10,000-11,000 tons of lobster are caught and more than $300 million is made per year off of this industry. It is considered to be the oldest and the best managed fishery in the world. This fishing is done off the coast of Western Australia between November and June every year. The fisheries target the whites, the lobsters that are freshly molted, as they are leaving the shallow reef areas. (Holthius, 1991; Department of Fisheries, 2000; Imgrund, 1999/2000)

The species is marketed fresh, but the greatest percentage of them is exported as frozen tails. (Holthius, 1991)

Economic Importance for Humans: Negative

Western rock lobsters do not really have a negative impact on humans economically, but it appears as though it is leading to that. This is because there is such a high demand around the world for lobster, and the lobster fisheries around the world are being pushed to their limits to meet the demand. It is predicted that because of this exploitation, some fisheries may fail in some countries within the next five years because of over fishing in those areas. More focus is now being placed on trying to grow lobsters in captivity in order to boost production while simultaneously keeping the population of wild lobsters safe. (Nexus, 2002)

Conservation Status

Humans may affect the lobsters greatly, but they also help them to flourish so that the population is not depleted. For example, the fisheries: limit the fishing season, have a minimum size requirement for the caught lobsters, offer protection for the breeding females, limit how many lobsters each fisherman can take, and restrict the size of the lobster pots. (Holthius, 1991; Imgrund, 1999/2000)

Other Comments

Panulirus cygnus has many common names: lobster, homard, yabbie, and in Australia it is called a crayfish. They are called crayfish in Australia because they resemble a common crayfish in color, size, and shape. Also, there is a meaning behind the name Panulirus cygnus. Panulirus was a Greek mythological skipper who fell asleep while at sea. He fell overboard and drifted on the sea for days only to land on the shores of Italy and be butchered. It is said that his body was left unburied so his spirit could not cross the river Styx into heaven and was condemned to roam the sea always being able to see land, but never being able to come ashore. (Imgrund, 1999/2000; Monchaux, n/a)

Contributors

Glossary

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

food

A substance that provides both nutrients and energy to a living thing.

internal fertilization

fertilization takes place within the female's body

macroalgae

seaweed. Algae that are large and photosynthetic.

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

nocturnal

active during the night

omnivore

an animal that mainly eats all kinds of things, including plants and animals

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polygynous

having more than one female as a mate at one time

reef

structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

Holthius, L. 1991. Marine Lobsters of the World: an annotated and illustrated catalogue of species of interest to fisheries known to date. Rome: Food and Agriculture Organizations of the United Nations.

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The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.

This material is based upon work supported by the
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Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.